The invention relates to the determination of the flight parameters of flying vehicles or to other fields of science and technology which deal with flows of liquid and gas.
The measurement of flight parameters is one of the most important problems in the aeromechanics and aerodynamics of flying vehicles (FVs). At the present time, to measure flight parameters (flow parameters) use is made of Pitot-Static tubes (PSTs) which are frequently mounted directly on the fuselage of the aircraft or the body of some other flying vehicle, and which actually measure the parameters of local flow close to a planar flow. As a rule, some of these PSTs which measure local flow parameters are mounted on the flying vehicles. The actual flight parameters are determined on the basis of prior calibrations.
A Pitot-Static tube is known from WO 94/02858. The known PST is mounted on the body or fuselage of an FV and has a cylindrical tube which is mounted on a strut having curved leading and trailing edges which come together when approaching from the base of the strut to the tube. The leading edge of the strut can be rounded. The Pitot-Static tube has orifices in the nose part of the tube for sensing the total pressure and orifices for sensing the static pressure at a certain distance from the nose of the tube. The Pitot probe has a heater for preventing the formation of ice. However, this PST cannot be applied to determine the angle of attack, since it lacks orifices for sensing pressure with the aid of which the angle of attack can be measured. Strictly, as follows from WO 94/02858, this Pitot probe is not designed for these purposes. Moreover, the convergence of the strut in a side view when the tube is approached leads to a sharp rise in the relative thickness of the profiles of the cross sections of the strut, while maintaining the internal volumes required for constructing the pneumatic paths and heaters. At high subsonic speeds (Mach number M=0.8-0.9), this leads to an earlier occurrence of local shock waves and a sharp rise in the shock-wave drag of such a Pitot-Static tube.
Another device for determining total pressure P0, static pressure Ps, and therefore also the Mach number M, as well as the angle of attack xcex1 is known from RU 2 000 561. Said device consists of a body constructed in the form of a plate sharpened at the front whose upper surface is arranged orthogonal to the axis of rotation and is equipped with orifices for measuring static pressure. Arranged in the rear part of the plate on its upper surface is a half-wing with a straight leading edge, which is orthogonal to the upper surface of the plate and on the end of which a total pressure probe is arranged. Orifices for measuring the angle of attack are arranged on the straight leading edge of the half-wing. Orifices for measuring the static pressure, the total pressure probe and orifices for measuring the angle of attack with the aid of corresponding pneumatic paths are connected to pressure transducers. The device is also equipped with a transducer for the angular displacement of the body. The orifices for measuring static pressure can be arranged on a non-rotating disc constructed flush with the upper surface of the plate. In essence, this device combines within itself the functions of an aerodynamic-angle transducer and a Pitot-Static tube. The given device has a number of disadvantages. Firstly, there is the complexity of design, which is caused firstly by the fact that the device is a rotating one. Consequently, it must be equipped with bearings with a very low coefficient of friction, it being necessary for the device to be statically and dynamically balanced. Moreover, it must be equipped with a transducer for the angular displacement of the body. The second disadvantage which, in essence, follows on from the first is an increased design weight. It is also a disadvantage of the given device that because of its design features it is impossible for the total pressure to be transmitted to the fuselage of the flying vehicle, to different consumers, and such a need frequently exists, with the aid of non-rotating pneumatic paths. Transmitting pressure from a rotating part of a device onto a non-rotating one requires the application of special seals and leads to complication of the design and a rise in its weight, to an increase in the friction-force moment and, consequently, to a rise in the minimum magnitude of the rate at which such a device starts to operate.
U.S. Pat. No. 4,378,696 teaches a fuselage PST for determining flight (flow) parametersxe2x80x94the angle of attack xcex1total pressure P0 and static pressure Ps and, consequently, Mach number M, which is an elongated axially symmetric body with a conical or ogival head part, where orifices for sensing total pressure are arranged, which merges into a circular cylinder on the surface of which orifices for sensing static pressure are arranged. Furthermore, this cylindrical surface merges into a conical one on which there are arranged orifices for sensing pressure in accordance with which the angle of attack is set, and thereafter into a cylindrical one again. For the purpose of being fastened to the fuselage or to the body of the FV, the Pitot probe has a strut whose cross section has a lenticular profile with a sharp leading edge
The disadvantages of the given PST are:
increased overall dimensions of the axially symmetric body;
complexity of design
increased aerodynamic drag;
increased required power of the heating anti-icing system;
low sensitivity of pressures measured in orifices arranged on the conical part (and intended for determining xcex1, in terms of the angle of attack, and this leads to larger errors in the determination of the angle of attack; and
increased design weight.
This is caused by the following factors:
1. The given PST has an enlarged mid-section of the axially symmetric body. The enlarged dimension of the mid-section is caused in this case by two circumstances.
Firstly, the cylindrical part of the axially symmetric body merges into a conical one on which there are arranged orifices for sensing pressure by means of which the angle of attack is determined. In order to somewhat enhance the sensitivity of the pressure sensed by means of these orifices in accordance with the angle of attack, the cone angle must be sufficiently large, and this leads to the necessity of significantly increasing the diameter of the axially symmetric body downstream of the given conical part. The second circumstance is associated with the fact that although the groups of orifices for measuring pressure, by means of which total pressure, static pressure and the angle of attack are determined, are dispersed in the given configuration, they are all still located on the same axially symmetric body. It is necessary to arrange inside it pneumatic paths, which go out from all the indicated groups of orifices, and also tubular electric heaters (TEHs) of the anti-icing system. The diameters of the pneumatic paths and of the TEHs cannot be less than certain minimum values which are determined for the pneumatic paths by the magnitude of the hydrodynamic lag, and for the TEHS by the maximum values of the heat flux density and the temperature of the surface of the heaters. The result is a high design saturation, that is to say a high design complexity of the axially symmetric body of the PST.
The circumstances indicated lead to an enlargement of the area of the mid-section, and thus to a rise in the design weight, the aerodynamic drag and the power of the anti-icing system. It is also necessary to note that the transition from a cylindrical part to a conical one, and thereafter to a cylindrical one again can lead to flow separation downstream of the conical part and to an earlier appearance (in terms of the Mach number) of local shock waves. In its turn, this must lead to a rise in aerodynamic drag. Moreover, an enlarged diameter of the axially symmetric body and the non-optimum shape of its aerial part in conjunction with the strut also produces unfavourable aerodynamic interference (flow separation and an earlier appearance of shock waves) in the region of the joint of the tapering tail part of the axially symmetric body of the PST downstream of the line of maximum thickness of the lenticular aerodynamic profile of the strut. This also leads to a certain increase in the aerodynamic drag of such a PST.
2. Increased length of the axially symmetric body. This is caused by the fact that all three groups of orifices are arranged on the axially symmetric body: for measuring the total and static pressure and the angle of attack. In this case, the orifices for measuring static pressure must be located sufficiently far from the strut so that measurements of the static pressure are accurate (without the introduction of corrections) and so that the over-pressure from the strut is virtually excluded. This leads to a significant increase in the length of the axially symmetric body. As is known, the formation of ice on a flying vehicle takes place, in the first instance, in regions adjoining regions of flow deceleration. [sic] (see, for example, Bragg M. B., Grigoreh G. M., Lee J. D. Airfoil Aerodynamic in Icing Conditions. J. Aircraft, vol. 23, N1, 1986). Such a region on the axially symmetric body of the PST is the nose region, and also, in the case of angles of attack differing from zero, the region in the vicinity of the line of the spread of flow on the windward part of the axially symmetric body of the PST. Consequently, quite massive tubular electric heaters are arranged inside such an elongated axially symmetric body over its entire length. This leads to a significant rise in the power required for heating, and also to an additional increase in the design weight, since the TEffs are quite massive. It should also be noted that the presence of a conical part on the axially symmetric body of the PST leads to the implementation of an additional overpressure effect on the cylindrical part situated at the front, where the orifices for measuring static pressure are arranged. As a result, the accurate determination (without the introduction of corrections) of the static pressure requires the orifices for sensing it to be located sufficiently far from this conical part. This leads to the necessity of additionally increasing the length of the axially symmetric body, something which also leads to a certain additional increase in the design weight, and requires additional power for the electrically heated anti-icing system.
3. The electric heaters arranged inside the strut of the PST for preventing the formation of ice on its leading edge, and therefore for preventing the influence of this ice on the measurement of the pressure on the axially symmetric body, are not used with adequate effectiveness, in the sense that they heat the strut on which no orifices for measuring pressure are arranged. This leads to a significant rise in weight and the electric power consumed.
The aim of the invention is to eliminate the disadvantages enumerated above.
The technical result consists of the following:
reduction in the aerodynamic drag of the strut and the axially symmetric body of the PST;
reduction in the power required for the heated anti-icing system;
design simplification;
reduction in the overall dimensions of the axially symmetric body; and
lowering of the design weight.
The technical result is achieved by virtue of the fact that the Pitot-Static tube including three groups of orifices for determining the total pressure, static pressure and angle of attack, an axially symmetric body and a strut for fastening to pneumatic paths arranged between them and to electric heating elements of the anti-icing system is constructed in such a way that the orifices for measuring the static pressure are arranged on a plate up-stream of the strut.
To advantage, the orifices for determining the angle of attack are arranged on the strut. Said orifices are arranged on said strut between its nose and a position of its maximum thickness. Accordingly, the orifices are arranged in a region X=0 . . . XC, wherein XC is a position of maximum thickness. XC is determined by the following equation:
C(XC)xe2x89xa6C(Xxe2x89xa0XC)
wherein C(X) is the profile thickness at a distance X from the profile nose.
For the purpose of an even greater reduction in the aerodynamic drag of the fuselage of the probe, the tail part of the axially symmetric body can terminate and mate smoothly with the aerodynamic profile of the strut in the region of its maximum relative thickness.
It is sometimes expedient, starting from design considerations, or from aerodynamic ones, to measure the static pressure on the FV at one point thereof, and to measure the total pressure and angle of attack at another. It is possible in this case for measurement purposes to apply the proposed fuselage probe, in which the plate with the orifices for measuring static pressure is constructed separately from the axially symmetric body with the strut.
For the purpose of application to supersonic flight regimes of the FV, when a very narrow range of angle of attack is required, the cross sections of the strut can have an aerodynamic profile with a sharpened nose.
For the purpose of application to FVs which are being used at subsonic M numbers, the cross sections of the strut can have a subsonic aerodynamic profile with a rounded nose.
For the purpose of widening the range of measurements of the angle of attack, the external surface of the strut can take the form of a cylindrical surface.
For the purpose of additionally widening the range of measurements of the angle of attack, the orifices for measuring the angle of attack can be arranged on the strut from its nose up to the maximum thickness.
For the purpose of an even greater reduction in the power required for the anti-icing system, the electric heating elements of the anti-icing system can be offset towards the leading edge of the strut.
In a preferred embodiment, the orifices for determining the angle of attack are arranged on the strut above the axially symmetric body in relation to the base of the MM Such an arrangement permits
enhancement of the accuracy of determination of the angle of attack; and
enhancement of the accuracy of measurement of the static pressure for transonic flow regimes.
Additionally, said arrangement permits a reduction in the influence of the angle of slip on measurement of the local angle of attack. This is achieved by virtue of the fact that the vortex wake from the axially symmetric body given slippage of the FV does not fall into the orifices for measuring the angle of attack.
Since the aerodynamic drag of the axially symmetric body for a zero angle of attack of the PST, and for high subsonic or supersonic speeds is proportional to the area of its mid-section, the lowering of the aerodynamic drag of the PST, were it to have the same shape as the prior-art PST, would also be proportional to the difference of the squares of the diameters of the axially symmetric body of the prior-art PST and the proposed PST. However, since the shape of the axially symmetric body of the proposed PST has no additional steps (conical step with subsequent thickening) as in the case of the prior-art PST, there will be no flow separation on it nor the appearance of shock waves downstream of the conical step. Thus, the lowering of the aerodynamic drag will be even greater. At large angles of attack, the lowering of the drag will also be very significant due to the fact that the length of the axially symmetric body on the proposed PST is substantially less than on the PST example of the prior art. Since there is no need to feed power for heating the plate on which the orifices for measuring static pressure are situated, in the case of the proposed PST because of its lack of conditions for icing (there being no regions of flow deceleration on it), and the required power for heating the strut on which the orifices for determining the angle of attack are situated is approximately equal to the required power for heating the strut of the prior-art PST, the lowering of the power required to heat the proposed PST is determined by the lowering of the power for heating the axially symmetric body. This lowering is proportional to the difference between the areas of the external surfaces of the axially symmetric body of the prior-art PST and the proposed PST (given the same temperature of their surfaces). Because the power required to heat the axially symmetric body of the prior-art PST is approximately equal to the power required by the strut, as a result, according to approximate estimates, the power required by the electric heaters on the proposed PST can be lowered by approximately 50% by comparison with the prior-art PST. Since the staggering of the orifices on the plate for measuring static pressure without the introduction of corrections to the overpressure relative to the base of the strut of the PST and, on account of its sweep, can be appreciably reduced by comparison with the corresponding orifices of the prior-art PST on the axially symmetric body, the weight of the plate and the axially symmetric body of the proposed PST can, as indicated by preliminary design studies, be approximately equal to the weight of the external shell of the axially symmetric body of the prior-art PST. As a result, the lowering of the design weight of the proposed PST occurs only by virtue of the lowering of the mass of the heaters in the axially symmetric body. This lowering of the weight is approximately 15-20% of the weight of the PST.
When the axially symmetric body is constructed in such a way, that its tail part terminates and merges smoothly with the strut in the region of its maximum thickness, the interference of the axially symmetric body and strut improves, and there is an additional substantial reduction in the aerodynamic drag of the PST because of the absence of an additional diffuser. In the case when for design, aerodynamic or some other considerations, the plate on the FV has to be situated on the fuselage at a location where the static pressure is implemented, while the strut with the axially symmetric body of the PST has to be situated at a different location, the plate with the orifices for measuring static pressure is constructed separately from the axially symmetric body with the strut. For the purpose of additionally reducing the drag on supersonic FVs when there is a need for a sufficiently narrow range of measurements of the angle of attack, the cross sections of the strut can have an aerodynamic profile with a sharpened nose. When the PST is applied on an FV which is employed at subsonic Mach numbers M, for the purpose of additionally reducing the drag and widening the range of measurements of the angle of attack, the cross sections of the strut can have a specialized subsonic aerodynamic profile with a rounded nose. For the purpose of an additional widening of the range of measurements of the angle of attack, the external surface of the strut can be in the form of a cylindrical surface. For the purpose of an additional widening of the range of measurements of the angle of attack, the orifices for measuring the angle of attack can be arranged on the strut away from its nose up to the maximum thickness. Because of the offset of the electric heating elements towards the leading edge of the strut, there is an additional substantial reduction in the useless heat losses by comparison with the prior-art PST, and reduction in the power required for heating.
For the purpose of enhancing the accuracy of determination of static pressure at transonic flow speeds, the aerodynamic profile of the strut can have an exit section on which at least one additional orifice for tapping the static pressure is arranged. For the purpose of simplifying the design and reducing the aerodynamic drag, the strut can be an element of the actual air frame proper of the FV.
By virtue of the fact that the influence of variation in the angle of attack on the magnitude of the pressures measured on the aerodynamic profile is substantially higher than on a cone, the error in the measurement of the angle for the proposed PST is substantially lower than for the prior-art PST, particularly when the orifices are arranged near it.
Moreover, owing to the transfer of the orifices for measuring the angle of attack from the axially symmetric body onto the strut there is a substantial simplification in the design of the axially symmetric body, and a reduction in its diameter and aerodynamic drag.
The reduction in the aerodynamic drag of the strut is achieved by applying the appropriate (subsonic or supersonic) aerodynamic profile. Owing to the offsetting of the electric heaters of the anti-icing system towards the nose of the profile of the strut, which is most subject to icing, it is possible to substantially reduce the power required for heating. Since the phenomenon of transonic stabilization of pressures is lacking in the region of the exit section of the aerodynamic profile, the presence of the orifices for tapping static pressure in the exit section can substantially enhance the accuracy of measurement of the pressure in the case of transonic flow speeds. Arranging the orifices for tapping static pressure on a special plate on the surface of the fuselage also substantially simplifies the design of the
PST, and can lower the power required for the anti-icing system, since this substantially simplifies the axially symmetric body, and the plate is not so subject to icing as is the axially symmetric body.